Voltage island chip implementation

ABSTRACT

A method and structure for designing an integrated circuit chip supplies a chip design and partitions elements of the chip design according to similarities in voltage requirements and timing of power states of the elements to create voltage islands. The invention outputs a voltage island specification list comprising power and timing information of each voltage island; and automatically, and without user intervention, synthesizes power supply networks for the voltage islands.

BACKGROUND OF THE INVENTION

The present invention generally relates to integrated circuits and moreparticularly to an improved integrated circuit design and method whichutilizes voltage islands that operate at independent voltages and can beselectively gated to reduce power consumption.

DESCRIPTION OF THE RELATED ART

As technology scales for increased circuit density and performance, theneed to reduce power consumption increases in significance as designersstrive to utilize the advancing silicon capabilities. The consumerproduct market further drives the need to minimize chip powerconsumption.

The total power consumed by conventional CMOS circuitry is composed oftwo primary sources. The first is active power consumed by circuits asthey switch states and either charge or discharge the capacitanceassociated with the switching nodes. Active power represents the powerconsumed by the intended work of the circuit to switch signal states andthus execute logic functions. This power is not present if the circuitin question is not actively switching. Active power is proportional tothe capacitance that is switched, the frequency of operation, and to thesquare of the power supply voltage. Due to technology scaling, thecapacitance per unit area increases with each process generation. Thepower increase represented by this capacitance increase is offset by thescaling of the power supply voltage, Vdd.

The frequency of operation, however, increases with each generation,leading to an overall increase in active power density from technologygeneration to technology generation. This increasing power density inturn drives the need for more expensive packaging, complex coolingsolutions and decreased reliability due to increased temperatures. Inaddition to active power, there are components of leakage power, themost dominant of which is the sub-threshold current of the transistorsin the circuit. As silicon technologies advance, smaller geometriesbecome possible, enabling improvements of device structures includinglower transistor oxide thickness (Tox), which in turn increasestransistor performance. To maintain circuit reliability, Vdd must belowered as Tox is reduced. As Vdd is reduced, the transistor thresholdvoltage (Vt) must be reduced in order to maintain or improve circuitperformance, despite the drop in Vdd. This decrease in Vt and Tox thendrives significant increases in leakage power, which has previously beennegligible. As silicon technologies move forward, leakage currentsbecome as important as active power in many applications. Therefore,there is a need for a method and structure that increases performance,while at the same time decreases power consumption. The inventiondescribed below satisfies these needs.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodof designing an integrated circuit chip that supplies a chip design andpartitions elements of the chip design according to similarities involtage requirements and timing of power states of the elements tocreate voltage islands. The invention outputs a voltage islandspecification list that can include power, simulation, reliability,floorplanning, and/or timing information of each voltage island. Theinvention simulates the chip design using an unknown voltage statepropagation on voltage island cell outputs identified by a power-on/offcontrol signal within the voltage island specification list.

The invention also provides a method of designing an integrated circuitchip that supplies a chip design and partitions elements of the chipdesign according to similarities in voltage requirements and timing ofpower states of the elements to create voltage islands. The inventionoutputs a voltage island specification list that has power and timinginformation of each voltage island and automatically, and without userintervention, synthesizes power supply networks for the voltage islands.

The invention performs physical placement of circuit elements on theintegrated circuit chip according to a hierarchy established in thevoltage island specification list. During the physical placementprocessing, limits are placed upon inserting logic elements within thevoltage islands. The invention performs routing physical wiring withinthe integrated circuit chip according to a hierarchy established in thevoltage island specification list. The invention constrains placement ofphysical pins to edges of the voltage islands adjacent power rings of apower supply within the integrated circuit chip. The specification listcan include a power source name, a power source type, minimum voltagelevel, maximum voltage level, nominal voltage level, switching signalname, switching signal type, power on hours, and/or steady state onpercentage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of a preferredembodiment(s) of the invention with reference to the drawings, in which:

FIG. 1 is a schematic diagram of a chip containing a voltage island,according to the invention;

FIG. 2 is a schematic diagram illustrating one embodiment of theinvention;

FIG. 3 is a schematic diagram illustrating the processing occurring initem 200 in FIG. 2;

FIG. 4 is a schematic diagram of waveforms illustrating the processingoccurring and item 302 in FIG. 3;

FIG. 5 is a schematic diagram of the waveform illustrating theprocessing occurring in item 304 in FIG. 3;

FIG. 6 is schematic diagram of voltage sets and illustrates theprocessing occurring in item 306 in FIG. 3;

FIG. 7 is a schematic diagram of voltage combinations and illustratesthe processing occurring in item 308 in FIG. 3;

FIG. 8 is a flowchart illustrating the processing occurring in item 310in FIG. 3;

FIG. 9 is a flowchart illustrating the processing occurring in item 202in FIG. 2; and

FIG. 10 is a flowchart illustrating the processing occurring in item 204in FIG. 2.

FIG. 11 is a schematic diagram of the front end voltage island designflow;

FIG. 12 is a schematic diagram of the back end voltage island designflow;

FIG. 13 is a schematic diagram illustrating a voltage island designusing peripheral wire bonds;

FIG. 14 is a schematic diagram illustrating a voltage island designusing C4 pads;

FIG. 15 is a schematic diagram illustrating a voltage island design fortest synthesis; and

FIG. 16 is a schematic diagram illustrating a voltage island physicaldesign optimization.

DETAILED DESCRIPTION OF THE INVENTION

The power challenges posed by advanced technologies force systemdesigners to make choices concerning device structures and voltagelevels for the functions they are designing. In previous generations,large functional blocks were not integrated on the same chip, so thesechoices could be made independently for each block. High levels ofintegration supported by system-on-a-chip (SoC) enabling technologydrive single chip implementations, where traditional approaches to powerdistribution and performance optimization fail to provide theflexibility of voltage and technology optimization of the previouslydisintegrated solution.

The invention divides each semiconductor chip into individual functionalblocks (voltage islands). These voltage islands of the SoC design canhave power characteristics unique from the rest of the design and, withthe invention, can be optimized accordingly.

An SoC architecture based on Voltage Islands uses additional designcomponents to ensure reliable communications across island boundaries,distribute and manage power, and save and restore logic states duringpower-off and on. FIG. 1 illustrates the multiple power sources usedwith the inventive voltage islands. More specifically, FIG. 1illustrates power structures 110 (VDDO) external to the voltage island120 as well as power structures 122 (VDDI) internal to the voltageisland 120. Item 121 represents standard logic within the island 120.Item 123 represents rebuffering cells. Item 124 illustrates a region ofstate-saving latches 125 used to store logic states during power-offperiods. In addition, a receiver 126 and driver 127 are also illustratedin FIG. 1. The Voltage Island 120 represents a level of hierarchy withunique powering that exists within a parent block 111 which constitutesa physical region in which the island 120 is placed. An island′ parentblock may be the top level of a chip design or even another island atthe next highest level of chip hierarchy.

As shown in FIG. 1, the circuits within a Voltage Island are primarilypowered from the island voltage, called VDDI (VDD-island or VDD-inside),while the circuits in the parent terrain are powered from a supplyvoltage called VDDO (VDD-outside). deeper hierarchy, the VDDO of oneisland may be equivalent to the VDDI of a parent island in which it iscontained.

The relationship between the voltages (VDDI and VDDO) of an island 120and its parent block 111 may vary considerably depending on how VoltageIslands are employed. For example, a dynamically powered island mighthave VDDI greater than VDDO when operating at maximum performance, VDDIless than VDDO when operating at reduced performance or to preservestates, and VDDI=0 V when fully powered down for standby currentcontrol.

Voltage variation present a problem for traditional, staticcomplementary metal oxide semiconductor (CMOS) logic gates. When such agate operates at a voltage sufficiently lower than the gate it drives,signal margins and performance will degrade, and the driven circuit willconsume significantly higher power. Further increases in the voltagedifference will eventually result in unreliable signal switching.Additional circuitry 123 is used to handle the differences in bothmagnitude and timing that can occur between VDDI and VDDO at islandboundaries. Receivers 126 perform this function for signals going fromthe parent block into the island, while driver cells 127 perform theequivalent for signals from island to the parent block. These driversand receivers provide reliable voltage level shifting from VDDI and VDDOfor a wide range of operating voltages, and do so with minimal impact tosignal delay or duty cycle.

In applications where VDDI or VDDO are allowed to assume voltage valuesbelow those necessary to support reliable signal switching, the VoltageIsland boundary also includes functions to disable communications acrossisland boundaries and provide reliably controlled states (eg. logic 0,logic 1, or hold last active state) to downstream logic. Such anoperation, known as fencing, prevents the undesired propagation ofunknown (X) states by powered-off logic.

Many possibilities exist for powering Voltage Islands. VDDI or VDDO maybe supplied directly from a unique, non-switched power distribution. Oneor both may be the output of an on-chip voltage regulator, whose voltagevalue may be fixed or programmable. Finally, VDDI or VDDO may be aswitched version of some other voltage supply, controlled by one or morePFET or NFET switches. A given SoC design may use one or more of theseapproaches depending upon the product design objectives.

Leakage or standby power can be reduced by lowering the voltage offunctionally-inactive islands well below the level required for reliableoperation. However, some subset of the logic state, prior to power-down,may need to be preserved to resume operation once the island is againpowered up, at the end of the inactive period. Special state-savinglatches 125 and rebuffering cells 123 provide a solution to thisproblem, eliminating the need to transfer logic states off-island andback in order to save and restore necessary logic states. Whereas astandard latch in a given island would operate from the island voltage(VDDI), a state-saving latch is a modification of the standard latch,adding both a VDDO connection and a state control input to selectbetween normal and state-saving operation. In normal operation, thestate-saving latch behaves identically to the standard latch. Instate-saving operation, the latch data is preserved in a portion of thelatch powered only by VDDO, and all other latch inputs (clocks, data,scan) are ignored. As long as VDDO remains active, VDDI may be powereddown without concern that unreliable logic levels will effect thelatch's logic state. State-saving latches are designed to consumeminimal power from the VDDO. The Voltage Island can be quickly returnedto normal operation once VDDI is restored via the latch state controlinput.

The invention designs chips with voltage islands using the generalprocessing shown in FIG. 2. More specifically, the invention partitionsthe design into voltage islands 200. In other words, the inventionanalyzes and evaluates the possible operating voltages and the timingsof power states of the different logical partitions to determine whichof these logical partitions can be combined into voltage islands. Thus,with the invention, the logical partitions are grouped according tosimilarities in voltage requirements and similarities in the timing ofpower states, to reduce overall power consumption of the chip.

The invention also performs floorplanning 202 and assessment 204 inorder to enable the writing of a voltage island specification list(speclist) 206. System requirements 208 are input to aid in thepartitioning 200. Similarly, the floorplan 210 is input into thefloorplanning operation 202. The assessment 204 determines whetheradditional partitioning is required (in which case processing returns tothe partitioning 200) or whether additional floorplanning is required(in which case processing returns to the floorplanning 202). Thespeclist produced is shown as item 212. The detailed operations involvedin partitioning 200 are further explained with respect to FIGS. 3-8. Thedetails of the floorplanning 202 are shown in FIG. 9 and the details ofthe assessment 204 are shown in FIG. 10.

The traditional process for the partitioning of an SoC design involvesdivision and subdivision into an n-level functional hierarchy. Theresulting functional components are grouped based upon minimizing thenumber and timing-criticality of signal that connect different groups.The chip area of each group is maintained between minimum and maximumsizes (high performance requirements may reduce maximum size of a group,and the need to limit floorplanning complexity may in turn limit minimumgroup size). Recently, the EDA industry has created a new wave of toolsintended to aid the designer in chip partitioning. The methods employedby these tools range from early SoC block-level planning, tophysically-aware gate-abstraction techniques, to quick placement of thenetlist for floorplanning insight.

Designing for Voltage Islands changes the traditional hierarchal logicalfunctional partitioning process into a hierarchy of voltage islands.When designing voltage islands, an optimal voltage for each functionalcomponent that minimizes active power at the required performance andcomponents whose voltage supply can be independently sequenced areidentified. Designing for voltage islands achieves a partitioningsolution that minimizes chip power within additional chip-levelconstraints including: maximum peak power, the available voltage rangeof each power source, and the maximum peak and average power for eachpower source.

The invention designs chips with voltage island using the generalprocessing shown in FIG. 2. More specifically, the invention partitionsthe design into voltage islands 200 and performs floorplanning 202 andassessment 204 in order to enable the writing of the speclist 206.System requirements 208 are input to aid in the partitioning 200.Similarly, the floorplan 210 is input into the floorplanning operation202. The assessment 204 determines whether additional partitioning isrequired (in which case processing returns to the partitioning 200) orwhether additional floorplanning is required (in which case processingreturns to the floorplanning 202). The produced speclist is shown asitem 212. The detailed operations involved in partitioning 200 arefurther explained with respect to FIGS. 3-8. The details of thefloorplanning 202 are shown in FIG. 9 and the details of the assessment204 are shown in FIG. 10.

To begin, the system requirements 208 that are supplied include thechip's (or SoC's) active power requirements, standby requirements, andavailable voltage supplies and levels. These define the maximum chippeak power, the number of latches per unit area that can act as statesaving latches (based upon average available wire tracks to be used forglobal voltage supplies), the minimum inactive time that a candidatecircuit can be powered-off (switching circuits on/off plus their on/offtime), as well as a voltage increment for analysis (e.g., algorithmmixed performance lever). Similarly, for each available alternate powersource and global Vdd, the system requirements identify the allowablevoltage range, the maximum average power, and the maximum be power.

Further, the system requirements identify the maximum number of uniquevoltage islands that should be contained in the chip and the maximumnumber of islands that can be powered on or off using a header switch.The system requirements also identify which chip-level available voltagesupplies can be power on or off at off-chip sources.

The system requirements also include data for each logic module and chipinput/output (I/O). Such data includes the chip area size; criticaltiming at each voltage within a set of allowable voltages for thetechnology and system; the switching waveforms between modes offunctional operation and times of functional in activity; and the activeand standby power requirements for each module or input/output for eachperiod of inactivity. The system requirements identify state-savinglatches 125 whose last date before inactivity must be present atresumption of activity, and a logic signal that uniquely identifies theperiod of inactivity. The system requirements define (for eachfunctional logic module) a list of allowable voltages for each module atwhich time requirements are met (positive slack), and a definition ofoperating modes in which the module is internally inactive (does notchange logic state).

Referring now to FIG. 3, the invention uses these inputs 208 in order topartition the chip into voltage islands. The partitioning processingbegins with item 300 which takes the initial logic partitions that areassigned prior to any voltage island partitioning. Next in item 302, theinvention defines switchable partitions and characterizes inactive andactive periods. The processing related to item 302 is shown in greaterdetail in FIG. 4 and is discussed below. Next, in item 304, theinvention identifies the voltage sets (per partition) that meet timingrequirements and also determines the power requirements (by period). Thedetailed processing of item 304 is shown in greater detail in FIG. 5 andis discussed below. In item 306, the invention determines whichchip-level combinations of partition voltage sets meet the timingrequirements. The detailed processing occurring in item 306 isillustrated and discussed below with respect to FIG. 6. In item 308, theinvention groups partitions by voltage source and assigns sources to thevarious voltage levels (in order to minimize power consumption). Thedetails of item 308 are shown and discussed below with respect to FIG.7. Finally, in item 310, in order to complete the partitioning, theinvention assigns groups to the various voltage islands. The details ofthe processing in item 310 are shown in FIG. 8 and are discussed below.

As mentioned above, FIG. 4 illustrates how the invention definesswitchable partitions and characterizes inactive and active periods. Twowaveforms 400, 404 are illustrated in FIG. 4. The upper waveform 400represents the active 410 and inactive periods 412 for a given module.The processing shown in item 402 modifies the waveform to classify theinactive periods 412 as either power-off inactive periods 414 orclock-gated inactive periods 416.

More specifically, in item 402, the invention determines whether eachinactive period 412 is less than a minimum inactive time. While oneembodiment of the invention identifies one possible limit (averagelatches per unit area) and one possible method for maximizing the amountof inactive time that meets this limit, the invention is not limited tosuch methods and, instead, is intended to broadly include any method ofidentifying the set of inactive periods. The minimum inactive time isestablished by the designer and controls the granularity of the process.

If the inactive period is less than the minimum inactive time, clockgating is assigned to this inactive period. Otherwise, for thoseinactive periods that exceed the minimum inactive time, a power offsignal can be assigned. As discussed above, by utilizing a power offsignal, the voltage leakage associated with clock gated inactive periodsis avoided.

Further, the invention maximizes power savings by utilizing thepower-off signal for as many inactive periods as possible. The inventiondoes this by first classifying those inactive periods below the minimuminactive time as a candidate inactive periods. Then, the inventionassembles a set of required state-saving latches for each candidateinactive period. From this, the invention creates a composite list ofstate saving latches across all candidate inactive periods.

Next, the invention determines whether there is a sufficient number ofstate saving latches available to convert the clock-gated inactiveperiods into power-off inactive periods. If so, the invention convertsall such clock-gated inactive periods into power-off inactive periods.If there are insufficient state saving latches to convert all suchclock-gated inactive periods, the invention assigns the state savinglatches to the longest clock-gated inactive periods first. This allowsonly the shortest inactive periods to remain as clock-gated periods,while all longer inactive periods are converted to power-off inactiveperiods. In other words, the invention tries to convert all inactiveperiods 412 to power-off inactive periods 414. However, because of thelimited number of state saving latches available, some inactive periods412 (the shortest inactive periods) fail becoming power-off inactiveperiods and are assigned as clock gated inactive periods 416. Therefore,as shown in waveform 404, the invention revises the waveform 400 toinclude active periods 410, inactive periods that are clock gatecontrolled 416, and inactive periods that are power-off signalcontrolled 414.

As mentioned above, FIG. 5 illustrates the details of processing thatoccur in item 304 in FIG. 3. In item 500, the invention times eachpartition across allowable voltage ranges. The allowable voltage rangesare calculated from the system requirements. More specifically, theminimum and maximum voltage values incremented by the voltage incrementestablished in the system requirements establish the voltage levels atwhich each partition will be timed. Global voltages are only assigned tothe top-level partitions.

Arrow 502 indicates all voltage values that meet latch-to-latch path,latch-input/output path (PI), and input/output-latch path timingrequirements. Voltages that do not meet these path timing requirementsare not considered allowable voltage ranges. As indicated by arrow 506,this allows the invention to output a list of possible voltage sourcesthat can supply the voltage within the allowable voltage ranges (aslimited by the list of allowable voltage sources for each given moduleand the allowable voltage ranges of each source). Arrow 504 indicatesthat the invention extracts (characterizes) each path timing for each ofthe allowable voltage ranges. The invention is intended to include anymethod of characterizing a logic entity across a number of voltageoperating points for the latter purpose of determining whether aninterconnection of these modules and various combinations of the voltagepoints meets an overall chip performance goal.

As shown by arrow 508, the invention annotates the waveforms to includeinformation regarding estimated standby power and estimated active powerat each allowable voltage. For example, the estimated standby power isbased upon the area when power is on; however, no standby power would beconsumed when voltage is off. Similarly, active power would be zero or aminimum value during clock-gated inactive periods, and zero when thepower was off. Active power is based on area and clock frequency whennot clock-gated. In addition, if more detailed active power data isavailable (e.g., using a switching-based estimator from a simulationtool, etc.) this data is substitute for the above estimates.

As mentioned above, FIG. 6 illustrates the details of item 306 shown inFIG. 3. In FIG. 6, item 600 represents a list of all combinations ofmodules/top-level allowable voltages. In item 600, for example, logicalpartition D includes two timing-met partition voltage values VD1 andVD2. These combinations of allowable voltages are characterized by theirpath times. The invention runs a chip-level timing analysis on eachelement shown in item 600 based upon the characterizations of the logicmodules and of the top-level logic. Any elements that fail such achip-level timing analysis are removed from item 600. The remaining database of timing-met partition voltage values is output as indicated byarrow 604. Item 606 illustrates the chip-level power waveforms at eachchip-level voltage set for each logical partition (A-E).

FIG. 7 shows the processing occurring in item 308 in FIG. 3 in greaterdetail. More specifically, in item 700, for each valid partition voltagedetermined in step 306, the invention identifies a list of possiblevoltage sources. For example, the first valid partition voltage oflogical partition A (VA1) includes two possible voltage sources (1 and2) while the first valid partition voltage of partition B (VB1) includesthree possible voltage sources (1-3). In item 702, the invention updatesthe chip-level list of voltage combinations with possible voltagesources of each voltage to produce the data base shown as item 704.

For each of the voltage combinations shown in item 704, the inventionuses steady state waveforms for each module and top-level logic tocalculate for the chip, for global Vdd, and for each alternative voltagesource, the total average power across the waveform and the highest peakpower across the waveform. The invention eliminates from the list ofpossible voltage islands any element that fail any of the chip orvoltage source limits regarding the maximum power or maximum averagepower (as shown by arrow 708). Thus, as shown in item 706, the inventionidentifies which of the logical partition and voltage sourcecombinations consume the lowest average power.

This allows the invention to minimize average power. This is achieved byfinding the minimum chip peak power and for each power source and globalVdd, the minimum average active power consumed, the minimum averagestandby power is consumed, as well as the combined minimum averageactive and standby power, and minimum peak active and standby power.

As shown in item 310 in FIG. 3, the invention then assigns groups oflogical partitions to specific voltage sources to define the voltageislands. This processing is shown in detail in FIG. 8. Morespecifically, in item 800 the invention starts with the list of logicalpartitions and lowest power consuming voltage sources and groups allmodules with like voltage sources and similar power timing patterns intovoltage islands. In the examples shown in item 800, VA1(0), VC1(0) andVD2(0) are grouped together because they all utilize voltage source (0)which runs at X volts. In a similar manner the matching waveforms initem 606 are used to group logical partitions by similar on/off powertiming patterns.

Next, in item 802, the invention connects voltage sources as islandpower sources to corresponding partitions. In item 804, the inventionassigns the above-determined lowest power consuming voltage to eachvoltage source for each given island. The invention then connects theclock gate and power off signals for each island as shown in item 806.Finally, the invention connects the global Vdd to the state savinglatches in each island and connects all clock-gating signals to clockgating circuits and applies the same to corresponding clock nets, asshown in item 808.

As mentioned previously, item 202 in FIG. 2 illustrates thatfloorplanning occurs after the partitioning process 200 has beencompleted. FIG. 9 illustrates the floorplanning in greater detail. Morespecifically, in item 900, for each island, the invention determines thephysical shape (e.g., using a standard placement tool, RTL-basedfloorplan estimator, etc.) of each of the voltage islands. After that,for each island, the invention determines and places the power structure(grind or ring), again using a standard floorplanning tool, as shown initem 902. Then, the islands are placed and oriented (again using astandard planning tool) as shown in item 904. The placement andorientation of the islands is optimized for wiring decongestion andtiming. Finally, each of the islands is connected to their respectivepower sources, as shown in item 906.

After the floorplanning, the invention performs an assessment processwhich is described in item 204 in FIG. 2. FIG. 10 illustrates thisassessment processing in greater detail. More specifically, in items1000, 1006, 1010, and 1016, the invention measures chip standby power,chip active power, and voltage drop, and analyzes timing andwireability, respectively. After each of the forgoing assessment steps,in decision blocks 1002, 1008, 1012, 1018, the invention determineswhether the established structure violates or meets the variousrequirements. If the chip standby power or chip active powerrequirements are not met, the partitions are updated (as shown in item1004). If the measured voltage drop or the timing and wireability arenot acceptable, the floorplan is updated as shown in item 1014.

After the forgoing processing, as shown in item 206 in FIG. 2, theinvention writes the voltage island speclist to output the voltageisland speclist 212. More specifically, the voltage island speclist 212includes, for each partition (voltage island), the name and power sourcelist and type (pad, fatwire, etc.) of each power net. In addition, thevoltage levels (minimum, maximum, nominal) is also included in thevoltage island speclist. The switching signal and type (off chip, header(and instance or instance list), etc.) are also included in the voltageisland speclist. Further, the voltage island speclist includes the poweron hours, the steady state on percentage, and other similar information.

As mentioned above, the invention divides each semiconductor chip into ahierarchy of individual functional blocks (voltage islands). Thesevoltage islands of the SoC design can have power characteristics uniquefrom the rest of the design and, with the invention, can be optimizedaccordingly.

There are numerous scenarios where the inventive voltage islands canprovide design leverage. Often, the most performance-critical element ofthe design, such as a processor core, requires the highest voltage levelsupported by the technology in order to maximize performance. Otherfunctions which coexist on the SoC, such as memories or control logic,may not require this level of voltage, thereby saving significant activepower if they can be run at lower voltages. In addition, voltageflexibility allows pre-designed standard elements from otherapplications to be in a new SoC application. Further, some functions,such as embedded analog cores, require very specific voltages, and canbe more easily accommodated in mixed voltage systems.

In another example, the invention facilitates power savings inapplications more sensitive to standby power, such as battery powerfunctions. Commonly, complex SoC designs consist of a number of diversefunctions, only a few of which are active at any given time. Methodssuch as clock gating can be used to limit the active power from theseidling functions, but the leakage (or standby) power remains, and can besignificant in high performance technologies. With the invention, thepower supplies for these functions are partitioned into islands, so thatthe function can be completely powered off, thus eliminating both activeand standby components of power. With the invention, the management ofthe power is built into the architecture and logic design of the SoC, tohandle power sequencing and communication issues.

The inventive voltage island techniques do not replace all other methodsof power management, in fact voltage island concepts can complement andamplify the effectiveness of other techniques. For example, clock gatingcan provide as much as 20-30% power savings for high performancefunctions. Clock gating can continue to be used for shorter duration“nap states” within the voltage islands which can also be powered offfor longer duration “sleep states.”

In addition to pre-defining clock-gated and powered-off functionalislands, transition between the above mentioned “nap” and “sleep” statescan be managed dynamically, by power management built into thearchitecture and logic design of the SoC. For example, when an island isto be inactivated for an unknown period of time, it may enter a clockgating “nap” state which can be quickly restored to the active statewhen required, particularly important if island must operate with shortbut frequent bursts of activity. However, if the power management logicdetects that the island has been inactive for a long continuous periodof time, it may predict that inactivity will continue long enough tojustify entry to a powered-off “sleep” mode, thus providing furtherpower savings for islands which experience long but unpredictableinactive periods.

The use of multi-threshold libraries is becoming a common method fortrading-off active and standby power for a function. Low thresholddevices provide a performance advantage over higher thresholdtransistors, particularly at lower voltage. Using Low-Vt transistors canallow timing closure at a lower voltage level, which can be a greatsavings for overall active power. Low device thresholds also implyhigher levels of leakage current, however, which can be detrimental tostandby power sensitive applications. For this reason, logic librariesutilizing high threshold transistors can be used in logic paths withoutcritical timing. The higher voltage required to make these circuits meetperformance goals can be justified by the reduction in standby power. Inan SoC with varied performance and power requirements, these device andlibrary options can be intermixed to optimize the diverse functions.Voltage island architecture methods enhance the usefulness of suchmulti-threshold design techniques. An island can be created to run anactive power sensitive block with low Vt's at a lower voltage than therest of the design. In addition, using voltage islands, this leaky,low-Vt block can be shut off completely during sleep modes to eliminatestandby power. Similarly, functions which are “always on” can be held ata higher voltage to accommodate less “leaky” high-Vt transistors, or bepowered from a separate, back-up supply. This application can beextended to include any method of biasing the voltage of transistorswithin an island for performance at the expense of increased standbypower (forward biasing) or decreasing standby power at the expense ofreduced performance (back biasing).

Voltage islands can be used at different levels of the design hierarchyto amplify their effectiveness. A block which can be powered off couldexist within a larger block which is running at a unique voltage, forexample. Constructing a voltage island capability with a finehierarchical granularity can enable a large variety of usefulpermutations.

Thus, as shown above, a common logical and physical hierarchy is definedfor each voltage island during the voltage island design planning and isdescribed in the voltage island SpecList file. Then, each voltage islandis processed in application specific integrated circuit (ASIC) front-endand back-end chip design flows. The collection of implementationrequirements for voltage islands (voltage island SpecList) is used toprovide needed voltage island information to drive the automated voltageisland ASIC chip design implementation flows.

More specifically, shown in FIG. 11 is a “front end” flow of a chipimplementation that automatically produces gate level connections. Inother words, the processing flow shown in FIG. 11 is fully automated anddoes not require user intervention. The processing flow takes theinformation output in the voltage island specification list andautomatically creates gate level connections.

In FIG. 11, item 212 is the voltage island speclist. From the voltageisland speclist 212, the various minimum, maximum, and nominal voltagesassigned to the modules are shown as item 1108. The power on hours andpercentage on factors assigned to the modules in the voltage islandspecification list 212 are shown as item 114. Further, the partitionsidentified in the voltage island speclist 212 are shown as item 1120.

Item 1100 illustrates the feature of the invention that uses a testbench to effect an X-state (unknown state) on all of the island celloutputs when identified within the voltage island speclist 212 toindicate that a given voltage island will be in an “off” state. Thisallows the voltage island to be tested to determine whether X-statesignals are being propagated to logic outside of the voltage islandwhile the voltage island is in the “off” state (which would represent anerror). When a voltage island is turned off, X-states are forcedthroughout the voltage island for all cells operating at the island'svoltage level (global voltage (VDDG) powered cells are excluded fromthis action). Forcing these X-states helps to verify that all islandoutputs have been properly fenced. If state-saving latches (globalvoltage powered) are employed for island power-up state retention,forcing the X-states also verifies that state-saving latches usage isfunctionally correct with respect to the system design. The simulationmechanism that creates the forced X-states is a special testbench thatruns within the simulation tool, in conjunction with the design netlistand the functional test bench. The functional test bench is shown asitem 1104 and the register transfer level (RTL) description used in manyautomated design tools is shown as item 1106.

The synthesis engine is shown as item 1110 and uses the minimum,maximum, and nominal voltages assigned to the modules in the voltageisland specification list 1108 in order to create the pre-physicaldesign net list 1112. A static timing analysis 1116 is performed on thepre-physical netlist 1112, as is a power calculation 1118. Item 1122represents the chip initialization, scanning, testing and clock RIEpowering operations that are used to produce the physical design netlist 1124.

FIG. 12 illustrates the “back end” flow that automatically, and withoutuser intervention, establishes power networks in order to produce amanufacturing netlist. More specifically, the creation of the powernetworks is shown as item 1200. The power networks are designed to beconsistent with the requirements of the voltage island speclist 212. Thepre-physical design netlist 1112 is utilized by the chip initializationengine 1122 in order to create the physical design net list 1124. Oncethe physical design netlist 1124 is created, placement 1204 and routing1206 operations can be performed. Item 1208 represents the optimizationof the static timing analysis and physical design, while item 1210represents the checking which must be performed before the manufacturingnetlist 1212 can be output.

FIG. 13 is a schematic diagram illustrating an island random logic macro(RLM) module 1320 that includes receiver cells 1302 and driver cells1304 as well as voltage island represented in a register transfer level(RTL) description 1308. Items 1300 represent the chip input/outputsignal connections. Item 1310 represents a fatwire power supply. Thistype of power supply is useful with the peripheral wire bondimplementation shown in FIG. 13. Item 1312 represents a test enable (TE)signal and item 1314 represents a fenceN control signal. The testenables signal comprises a level sensitive scan design (LSSD) type oftest enable signal. The fenceN signal is a functional sleep mode controlsignal used for power sequencing. The island driver cells 1304 caninclude one of the following fencing modes, the fence 0 mode (whichforces the drivers 1304 to output 0), a fence 1 mode (which forces thedrivers 1304 to output 1), and a fense hold mode (which maintains theprevious logical state of the island driver cells 1304).

During the design entry phase, logic designers enter voltage islandreceivers and drivers. The receivers and drivers are, for example,single-ended level shifters. The island input RLM receivers have asingle input/output pair, while the islands output RLM drivers have thefollowing fencing capabilities: fence output to 0, fense output to 1,and fence hold output. When the fenceN signal is 0, the output driversare forced to their fenced value. Otherwise the drivers propagate theirinput-pin values to the voltage-island RLM outputs. The fenceN is aninput and on all single-ended voltage island output drivers. The TEsignal is an input pin on all “fence hold” driver types. The TE signalis a testability requirement for the fence-hold output drivers.

The TE and fenceN input signals are not level-shifted inside the voltageisland, so they do not require a single-ended receiver. Single-endedreceivers and fencing circuits require power from the voltage islandpower sources and the chip (global) power source VDDG to performvoltage-level translation at each RLM port. Some voltage islands have asparse global power source grid, in which case the single-endedreceivers or fencing cells can reside anywhere in the RLM. In theabsence of this grid, the cells should be placed near the global powersource power ring on the periphery of the RLM. FIG. 14 is similar to theschematic shown in FIG. 13; however, the structure shown in FIG. 14relates to C4 (copper pad) connections. More specifically, items 1400illustrates the power C4 pad connections.

The invention includes a library of data communications circuitsspecifically designed to enable communications across voltage islandsoperating at different voltages. The sensing circuits handle voltageisland communications when in the voltage island is powered down, andessentially establish a “known” state on the nets that connect otherpower islands the same circuits and also handle data communication whenthe voltage islands are powered up. Voltage island constraints arehandled by the design system checking, simulation, synthesis, testinsertion, physical-design optimization, placement, and power-routingtools.

FIG. 15 illustrates the design for test synthesis (DFTS) which requiresthe addition of test clocks and controls 1500 as well as the scan in(SI) 1502 and scan out (SO)1504 receivers and drivers. Such structuresenable consistent and easy testing of each voltage island individually,as well as testing all the voltage islands in combination. FIG. 16represents the physical design (PD) optimization. During theoptimization modifications to the voltage island are restricted. Morespecifically, changes within the voltage island are limited to minorpower rebuffering 1600 and similar modifications. Outside the voltageisland 1320, all standard optimization techniques 1602 can be appliedwithout restriction. By restricting the changes that can be made withinthe voltage island, the invention helps maintain the initial structurerequired by the voltage island specification list 212, which will besubstantially error free and provide the greatest power conservation.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

What is claimed is:
 1. A method of designing an integrated circuit chip,said method comprising: supplying a chip design; partitioning elementsof said chip design according to similarities in voltage requirementsand timing of power states of said elements to create voltage islands;outputting a voltage island specification list comprising at least oneof power, simulation, reliability, floorplanning, and timing informationof each voltage island; and simulating said chip design using an unknownvoltage state propagation on voltage island cell outputs identified by apower-on/off control signal within said voltage island specificationlist.
 2. The method in claim 1, further comprising performing a statictiming analysis using minimum, maximum, and nominal voltages for eachisland from said voltage island specification list.
 3. The method inclaim 2, wherein said performing of said static timing analysiscomprises, for paths communicating between two islands, usingminimum-to-minimum, maximum-to-maximum, minimum-to-maximum, andmaximum-to-minimum voltage values from said voltage island specificationlist to measure and optimize timing.
 4. The method in claim 1, furthercomprising performing a power calculation utilizing power-on hours and apercent-on factor for each island from said voltage island specificationlist.
 5. The method in claim 1, further comprising testing each islandindividually and said chip design as a whole.
 6. The method in claim 1,wherein said simulating comprises using a test bench to force saidvoltage island cell outputs to said unknown states when said controlsignal indicates said power-off condition.
 7. The method in claim 1,wherein said specification list comprises at least one of a power sourcename, a power source type, minimum voltage level, maximum voltage level,nominal voltage level, switching signal name, switching signal type,power on hours, and steady state on percentage.
 8. A program storagedevice readable by machine, tangibly embodying a program of instructionsexecutable by said machine for performing a method of designing anintegrated circuit chip, said method comprising: supplying a chipdesign; partitioning elements of said chip design according tosimilarities in voltage requirements and timing of power states of saidelements to create voltage islands; outputting a voltage islandspecification list comprising power and timing information of eachvoltage island; and simulating said chip design using an unknown voltagestate on inputs of a voltage island when a timing waveform within saidvoltage island specification list indicates a power-off condition withinsaid voltage island.
 9. The program storage device in claim 8, whereinsaid method further comprises performing a static timing analysis usingminimum, maximum, and nominal voltages for each island from said voltageisland specification list.
 10. The program storage device in claim 9,wherein said performing of said static timing analysis comprises, forpaths communicating between two islands, using minimum-to-minimum,maximum-to-maximum, minimum-to-maximum, and maximum-to-minimum voltagevalues from said voltage island specification list to measure andoptimize timing.
 11. The program storage device in claim 8, furthercomprising performing a power calculation utilizing power-on hours and apercent-on factor for each island from said voltage island specificationlist.
 12. The program storage device in claim 8, further comprisingtesting each island individually and said chip design as a whole. 13.The program storage device in claim 8, wherein said simulating comprisesusing a test bench to force said inputs to said unknown states when saidcontrol signal indicates said power-off condition.
 14. The programstorage device in claim 8, wherein said specification list comprises atleast one of a power source name, a power source type, minimum voltagelevel, maximum voltage level, nominal voltage level, switching signalname, switching signal type, power on hours, and steady state onpercentage.